In multiple-input multiple-output (MIMO) systems, linear precoding based spatial multiplexing is a promising technique. It provides higher data rate by enabling parallel multi-stream transmission in MIMO fading channels by exploiting the full or partial channel state information at the transmitter (CSIT), for example, the precoding matrix. For frequency division duplexing (FDD) systems, the precoding matrix is available via a finite-rate feedback channel through which the receiver sends the channel information to the transmitter periodically or aperiodically. For time division duplexing (TDD) systems, the precoding matrix may be available by exploiting channel reciprocity at the transmitter directly.
U.S. Patent Publication No. US2007/0206626A1, entitled “Apparatus and method for determining beamforming vector in a codebook-based beamforming system”, filed on Feb. 5, 2007, discloses that at the receiver in a codebook-based transmission beamforming system, forthcoming channel values for a forthcoming period are generated using M present and previous channel estimates by means of minimum mean square error (MMSE) filter, a.k.a, the Wiener filter.
In paper “Grassmannian predictive coding for delayed limited feedback MIMO systems,” T. Inoue and R. W. Heath, Jr., in Proc. 47th Allerton Conf. Commun., Contr., Comput. Sep. 30-Oct. 2, 2009, pp. 783-788, a receiver predicts the forthcoming channel direction along the geodesic passing through the present and previous channel direction observations with a long-term feedback optimal step size.
However, the method disclosed by U.S. Patent Publication No. 2007/0206626A1 badly depends on accurate estimation of the temporal correlation of the MIMO channel. With respect to the paper “Grassmannian predictive coding for delayed limited feedback MIMO systems,” it is designed for a beamforming system where only a single data stream is transmitted. Henceforth, it cannot handle spatial multiplexing where multiple streams are pending for parallel transmission.